Palladium‐Catalyzed Atom‐Transfer Radical Cyclization at Remote Unactivated C(sp³)−H Sites: Hydrogen‐Atom Transfer of Hybrid Vinyl Palladium Radical Intermediates

Abstract

A novel mild, visible‐light‐induced palladium‐catalyzed hydrogen atom translocation/atom‐transfer radical cyclization (HAT/ATRC) cascade has been developed. This protocol involves a 1,5‐HAT process of previously unknown hybrid vinyl palladium radical intermediates, thus leading to iodomethyl carbo‐ and heterocyclic structures.

Advances in Selected Heterocyclization Methods

“…Photoinduced TM-catalyzed radical reactions have also been employed toward the synthesis of heterocycles. In recent years, Gevorgyan reported the use of photoexcited palladium catalytic system to generate aryl, 36 vinyl, 37 and alkyl 38 radicals. 39 This catalytic system enabled the C–O bond cleavage of aryl triflates toward oxindoles 41 and isoindolin-1-ones 43 (Scheme 11 ).…”

[3+2] Cycloaddition of alkyl aldehydes and alkynes enabled by photoinduced hydrogen atom transfer

“…Initially, the excited-state catalyst *[W 10 O 32 ] 4− , obtained by photoexcitation of the decatungstate anion at 390 nm, abstracts a hydrogen atom from aldehydes to form acyl radicals I and [W 10 O 32 ] 5− H + . Subsequent radical addition to alkynes followed by 1,5-HAT of vinyl radicals [51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68] generates nucleophilic alkyl radicals III. Then, a polaritymatched addition at the β-carbon atom leads to radicals IV.…”

Visible Light‐induced Functionalization of C−H Bonds: Opening of New Avenues in Organic Synthesis

“…Gevorgyan and coworkers demonstrated a visible‐light‐induced HAT/ARTC cascade reaction for the formation of spiroannulated cyclopentane iodoalkyl carbo‐ and heterocyclic structure ( 25 ) from iodovinylbenzylic compounds ( 24 ) via 1,5 ‐ HAT process activated by hybrid vinyl palladium intermediates (Scheme 11). [52] …”

“…Gevorgyan and coworkers demonstrated a visible-light-induced HAT/ARTC cascade reaction for the formation of spiroannulated cyclopentane iodoalkyl carbo-and heterocyclic structure (25) from iodovinylbenzylic compounds (24) via 1,5-HAT process activated by hybrid vinyl palladium intermediates (Scheme 11). [52] A wide range of iodovinylbenzyl derivatives with heterocyclic moiety or aliphatic chains provided corresponding iodomethyl dihydrobenzofuran derivatives (25) in good yields. Iodomethyl group in the products thus obtained was further modified to cyanide, azide and exo-methylene group representing the synthetic applicability of the HAT/ARTC cascade products.…”